watchdog: use dig instead of check_dns (#6685)

* watchdog: use dig instead of check_dns

check_dns is slower and uses more system resources,
dig wrapped in a script is a more performant approach and uses
fewer system resources

* added debug mode + compose image bump

---------

Co-authored-by: maxi322 <maxi322@users.noreply.github.com>
Co-authored-by: DerLinkman <niklas.meyer@servercow.de>

data/Dockerfiles/watchdog/check_dns.sh

@@ -0,0 +1,39 @@
+#!/bin/sh
+
+while getopts "H:s:" opt; do
+  case "$opt" in
+    H) HOST="$OPTARG" ;;
+    s) SERVER="$OPTARG" ;;
+    *) echo "Usage: $0 -H host -s server"; exit 3 ;;
+  esac
+done
+
+if [ -z "$SERVER" ]; then
+  echo "No DNS Server provided"
+  exit 3
+fi
+
+if [ -z "$HOST" ]; then
+  echo "No host to test provided"
+  exit 3
+fi
+
+# run dig and measure the time it takes to run
+START_TIME=$(date +%s%3N)
+dig_output=$(dig +short +timeout=2 +tries=1 "$HOST" @"$SERVER" 2>/dev/null)
+dig_rc=$?
+dig_output_ips=$(echo "$dig_output" | grep -E '^[0-9.]+$' | sort | paste -sd ',' -)
+END_TIME=$(date +%s%3N)
+ELAPSED_TIME=$((END_TIME - START_TIME))
+
+# validate and perform nagios like output and exit codes
+if [ $dig_rc -ne 0 ] || [ -z "$dig_output" ]; then
+  echo "Domain $HOST was not found by the server"
+  exit 2
+elif [ $dig_rc -eq 0 ]; then
+  echo "DNS OK: $ELAPSED_TIME ms response time. $HOST returns $dig_output_ips"
+  exit 0
+else
+  echo "Unknown error"
+  exit 3
+fi